为什么 matplotlib 底图没有绘制我地图中某些区域的颜色？

Question

下面的代码应该为越南的所有州着色：

import pandas as pd
import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap

fig, ax = plt.subplots(figsize=(10,20))

# create the map
map = Basemap(resolution='l', # c, l, i, h, f or None
            projection='merc',
            lat_0=15.95, lon_0=105.85,
            llcrnrlon=102., llcrnrlat= 8.31, urcrnrlon=109.69, urcrnrlat=23.61)



# load the shapefile, use the name 'states'
map.readshapefile(r'path\to\gadm36_VNM_1', name='states', drawbounds=True)
# shapefile downloaded from http://www.gadm.org/  



# collect the state names from the shapefile attributes so we can
# look up the shape obect for a state by it's name
state_names = []
for shape_dict in map.states_info:
    state_names.append(shape_dict['VARNAME_1'])

ax = plt.gca() # get current axes instance



# NOR, CEN, SOU and MEK are some subdivisions I have created for the states of Vietnam 

NOR = ['Lai Chau',
'Lao Cai',
'Ha Giang',
'Cao Bang',
'Dien Bien',
'Son La',
'Yen Bai',
'Tuyen Quang',
'Bac Kan',
'Lang Son',
'Thai Nguyen',
'Phu Tho',
'Vinh Phuc',
'Hoa Binh',
'Ha Noi',
'Bac Ninh',
'Hai Duong',
'Hung Yen',
'Ha Nam',
'Quang Ninh',
'Hai Phong',
'Thai Binh',
'Nam Dinh',
'Bac Giang',
'Ninh Binh']



CEN = ['Thanh Hoa',
      'Nghe An',
      'Ha Tinh',
      'Quang Binh',
      'Quang Tri',
      'Thua Thien Hue',
      'Da Nang']



SOU = ['Quang Nam',
      'Kon Tum',
      'Quang Ngai',
      'Gia Lai',
      'Binh Dinh',
      'Dak Lak',
      'Phu Yen',
      'Khanh Hoa',
      'Dak Nong',
      'Lam Dong',
      'Ninh Thuan']




MEK = ['Binh Phuoc',
      'Dong Nai',
      'Binh Thuan',
      'Tay Ninh',
      'Binh Duong',
      'Dong Nai',
      'Ba Ria - Vung Tau',
      'Ho Chi Minh',
      'Long An',
      'An Giang',
      'Dong Thap',
      'Tien Giang',
      'Kien Giang',
      'Can Tho',
      'Vinh Long',
      'Ben Tre',
      'Hau Giang',
      'Tra Vinh',
      'Soc Trang',
      'Bac Lieu',
      'Ca Mau']



# Define the colours to be used to colour the states

from matplotlib import cm
from numpy import linspace

start = 0.5
stop = 1.0
number_of_lines= 4
cm_subsection = linspace(start, stop, number_of_lines)

cm_subsection[0] = cm_subsection[0]*4
cm_subsection[1] = cm_subsection[1]*0.6
cm_subsection[2] = cm_subsection[2]*0.8
cm_subsection[3] = cm_subsection[3]*0.1

colors = [ cm.Blues(x) for x in cm_subsection ]


for state in NOR:
    seg = map.states[state_names.index(state)]
    poly = Polygon(seg, facecolor=colors[0], edgecolor=colors[0])
    ax.add_patch(poly)

for state in CEN:
    seg = map.states[state_names.index(state)]
    poly = Polygon(seg, facecolor=colors[1], edgecolor=colors[1])
    ax.add_patch(poly)

for state in SOU:
    seg = map.states[state_names.index(state)]
    poly = Polygon(seg, facecolor=colors[2], edgecolor=colors[2])
    ax.add_patch(poly)

for state in MEK:
    seg = map.states[state_names.index(state)]
    poly = Polygon(seg, facecolor=colors[3], edgecolor=colors[3])
    ax.add_patch(poly)





import matplotlib.patches as mpatches

NOR_patch = mpatches.Patch(color=colors[0], label='Rate: 34.85%')
CEN_patch = mpatches.Patch(color=colors[1], label='Rate: 25.61%')
SOU_patch = mpatches.Patch(color=colors[2], label='Rate: 32.66%')
MEK_patch = mpatches.Patch(color=colors[3], label='Rate: 20.02%')
plt.legend(handles=[NOR_patch, CEN_patch, SOU_patch, MEK_patch])
plt.show()

但这会产生下面的地图，其中一些州没有着色，即使它们出现在州名和细分中：

事实上，如果我尝试为列表中不存在名称的状态着色，则会引发错误：

MEK.append('ABCDE')

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-619-a89da62a0831> in <module>()
    134 
    135 for state in MEK:
--> 136     seg = map.states[state_names.index(state)]
    137     poly = Polygon(seg, facecolor=colors[3], edgecolor=colors[3])
    138     ax.add_patch(poly)

ValueError: 'ABCDE' is not in list

因此，显然列表中存在未着色的状态，因为我没有收到任何错误。那么，发生了什么？

编辑：让我震惊的是，几乎所有没有颜色的州在现实世界中至少有一部分与海洋/海洋接壤。下面以红色突出显示 6 个例外：

现在这很有趣！会不会跟这个问题有关系？如果是，是什么？为什么？为什么存在这 6 个例外？

编辑 2： 我在绘制菲律宾地图时得到了类似的结果：

Answer 1

在shapefiles 中，一个国家/省/任何地方都可能被分解为几个线段。为什么会这样，我不知道，但为了正确绘制形状，您需要使用所有必要的段。实际上，在Basemap documentation for shapefiles 中有一个“填充多边形”下的示例，如何正确执行此操作。我根据您的用例调整了他们的示例。这可能不是最理想的解决方案，但它似乎有效。

import pandas as pd
import matplotlib.pyplot as plt
from mpl_toolkits.basemap import Basemap
from matplotlib import patches as mpatches
from matplotlib import cm
from numpy import linspace
import matplotlib.patches as mpatches
from matplotlib.collections import PatchCollection

fig, ax = plt.subplots(figsize=(4,8))

# create the map
map = Basemap(resolution='l', # c, l, i, h, f or None
            projection='merc',
            lat_0=15.95, lon_0=105.85,
            llcrnrlon=102., llcrnrlat= 8.31, urcrnrlon=109.69, urcrnrlat=23.61)

# load the shapefile, use the name 'states'
map.readshapefile(r'shapefiles/gadm36_VNM_1', name='states', drawbounds=True)
# shapefile downloaded from http://www.gadm.org/  

# collect the state names from the shapefile attributes so we can
# look up the shape obect for a state by it's name
state_names = []
for shape_dict in map.states_info:
    state_names.append(shape_dict['VARNAME_1'])

ax = plt.gca() # get current axes instance

# NOR, CEN, SOU and MEK are some subdivisions I have created for the states of Vietnam     
NOR = ['Lai Chau',
'Lao Cai',
'Ha Giang',
'Cao Bang',
'Dien Bien',
'Son La',
'Yen Bai',
'Tuyen Quang',
'Bac Kan',
'Lang Son',
'Thai Nguyen',
'Phu Tho',
'Vinh Phuc',
'Hoa Binh',
'Ha Noi',
'Bac Ninh',
'Hai Duong',
'Hung Yen',
'Ha Nam',
'Quang Ninh',
'Hai Phong',
'Thai Binh',
'Nam Dinh',
'Bac Giang',
'Ninh Binh']

CEN = ['Thanh Hoa',
      'Nghe An',
      'Ha Tinh',
      'Quang Binh',
      'Quang Tri',
      'Thua Thien Hue',
      'Da Nang']

SOU = ['Quang Nam',
      'Kon Tum',
      'Quang Ngai',
      'Gia Lai',
      'Binh Dinh',
      'Dak Lak',
      'Phu Yen',
      'Khanh Hoa',
      'Dak Nong',
      'Lam Dong',
      'Ninh Thuan']

MEK = ['Binh Phuoc',
      'Dong Nai',
      'Binh Thuan',
      'Tay Ninh',
      'Binh Duong',
      'Dong Nai',
      'Ba Ria - Vung Tau',
      'Ho Chi Minh',
      'Long An',
      'An Giang',
      'Dong Thap',
      'Tien Giang',
      'Kien Giang',
      'Can Tho',
      'Vinh Long',
      'Ben Tre',
      'Hau Giang',
      'Tra Vinh',
      'Soc Trang',
      'Bac Lieu',
      'Ca Mau']

# Define the colours to be used to colour the states    
start = 0.5
stop = 1.0
number_of_lines= 4
cm_subsection = linspace(start, stop, number_of_lines)

cm_subsection[0] = cm_subsection[0]*4
cm_subsection[1] = cm_subsection[1]*0.6
cm_subsection[2] = cm_subsection[2]*0.8
cm_subsection[3] = cm_subsection[3]*0.1

colors = [ cm.Blues(x) for x in cm_subsection ]

##collecting the line segments for the provinces:
patches = {state: [] for state in NOR+CEN+SOU+MEK}    
for info, shape in zip(map.states_info, map.states):
    for state in NOR+CEN+SOU+MEK:
        if info['VARNAME_1'] == state:
            patches[state].append(mpatches.Polygon(
                shape, True,
            ))

##coloring the the provinces by group:
for state in NOR:
    ax.add_collection(PatchCollection(
        patches[state], facecolor = colors[0], edgecolor=colors[0]
    ))

for state in CEN:
    ax.add_collection(PatchCollection(
        patches[state], facecolor = colors[1], edgecolor=colors[1]
    ))

for state in SOU:
    ax.add_collection(PatchCollection(
        patches[state], facecolor = colors[2], edgecolor=colors[2]
    ))

for state in MEK:
    ax.add_collection(PatchCollection(
        patches[state], facecolor = colors[3], edgecolor=colors[3]
    ))

NOR_patch = mpatches.Patch(color=colors[0], label='Rate: 34.85%')
CEN_patch = mpatches.Patch(color=colors[1], label='Rate: 25.61%')
SOU_patch = mpatches.Patch(color=colors[2], label='Rate: 32.66%')
MEK_patch = mpatches.Patch(color=colors[3], label='Rate: 20.02%')
plt.legend(handles=[NOR_patch, CEN_patch, SOU_patch, MEK_patch])
plt.show()

结果和预期的一样：

请注意，我只能在 Python 3.6 下测试代码，因此可能需要进行一些调整。希望这会有所帮助。